Block 3, the observation post of the Ouvrage de Fermont was called after Paul Doumer, the French president between 1931 and 1932. He was assassinated on 6th May 1932 by a Russian immigrant Paul Gorguloff while opening a book fair in Paris. The letters O.C. stand for Observatoire Cuirassé or Armoured Observation Post. In the older designs block 3 was often referred to with O.C.